FIELD OF THE INVENTION
The invention relates to a multiphase high-temperature material made from an alloy on the basis of an intermetallic compound of the Ti.sub.3 Al type, especially for use in heat engines such as internal combustion engines, gas turbines and aircraft engines.
The development of heat engines is increasingly directed towards higher outputs while keeping to the same size as far as possible, resulting in a steady increase in the thermal stress of the individual components, so that the materials being used are increasingly required to be both more heat-proof and stronger.
In addition to numerous developments in the materials sector, for example nickel-based alloys, alloys which are on the basis of an intermetallic compound of the Ti.sub.3 Al type, in particular, have attracted increasing interest with regard to such use in heat engines, because of the high melting point combined with low density. Numerous developments deal with the attempt to improve the mechanical properties of such high-temperature materials. Those developments, in addition to improving the mechanical properties, especially address the resistance to corrosive attack at high service temperatures, for example resistance to the attack of hot combustion gases, gaseous chlorides and sulphur dioxide.
Moreover, at lower temperatures the useful life is limited by condensed alkali metal sulphates and alkaline earth metal sulphates, preventing full utilisation of the per se available strength potential of such materials. In other words, the service temperature which could be achieved, in terms of high-temperature creep resistance per se, is reduced due to the limited oxidation resistance.
It is sufficiently well known that the oxidation resistance of the binary titanium/aluminum compounds is completely inadequate for the applications mentioned above, since the oxidation rate is several powers of ten higher than that of superalloys used at present, and their oxide layers have low adhesion, which results in steady corrosive erosion. It is known that compounds on a titanium aluminide basis having significant proportions of chromium and vanadium do exhibit good oxidation resistance at temperatures above 900.degree. C., which is comparable with that of superalloys used at present, but that oxidation behavior at lower temperatures is completely inadequate, comparable with that of binary titanium aluminides, e.g. Ti.sub.3 Al.
In the same way, the mechanical properties of those compounds are completely inadequate for industrial applications. At low temperatures they have virtually no ductility, and at enhanced temperatures they have inadequate creep resistance or limiting creep stress.
It is accordingly an object of the invention to provide a high-temperature, creep-resistant material, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which has both the desired mechanical properties and the required corrosion resistance.